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United States Patent |
5,271,486
|
Okamoto
,   et al.
|
December 21, 1993
|
Torque limiter
Abstract
A torque limiter having an outer ring with a plurality of cam surfaces and
spring supporting surfaces formed on an inner peripheral surface, an inner
member mounted in the outer ring, and a plurality of rollers mounted
between the cam surfaces and the inner member. Springs supported on the
spring supporting surfaces bias the rollers in a direction to bite into
the cam surfaces and the inner member. The springs have a predetermined
spring force which is sufficient to maintain the rollers in wedging
engagement between the cam surfaces and the inner member when a turning
torque for turning the inner member in a direction to urge the rollers out
of the wedging engagement is applied to the inner member, but only until
the applied torque reaches a predetermined value.
Inventors:
|
Okamoto; Yuji (Kuwana, JP);
Kataoka; Masahiko (Kuwana, JP);
Ichikawa; Kenichi (Kuwana, JP);
Itomi; Shoji (Kuwana, JP)
|
Assignee:
|
NTN Corporation (Osaka, JP)
|
Appl. No.:
|
702116 |
Filed:
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May 16, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
192/45; 464/30 |
Intern'l Class: |
F16D 007/06; F16D 041/06 |
Field of Search: |
192/45,41 R
464/30
|
References Cited
U.S. Patent Documents
2211053 | Aug., 1940 | Critchfield | 192/45.
|
2843238 | Jul., 1958 | Rozner | 192/45.
|
2902125 | Sep., 1959 | House et al. | 192/45.
|
3014567 | Dec., 1961 | Stockton | 192/45.
|
3031052 | Apr., 1962 | Blinder | 192/45.
|
3087589 | Apr., 1963 | Gorsky | 192/45.
|
3993176 | Nov., 1976 | Marola et al. | 192/45.
|
4178805 | Dec., 1979 | Mazzorana | 192/45.
|
4236619 | Dec., 1980 | Kuroda | 192/45.
|
4828086 | May., 1989 | Lederman | 192/41.
|
4852708 | Aug., 1989 | Parkhurst | 192/45.
|
Foreign Patent Documents |
1-158827 | Nov., 1989 | JP.
| |
Primary Examiner: Lorence; Richard M.
Attorney, Agent or Firm: Armstrong, Westerman, Hattori, McLeland & Naughton
Parent Case Text
This application is a continuation of application Ser. No. 489,587, filed
on Mar. 7, 1990, now abandoned.
Claims
What is claimed is:
1. A torque limiter comprising an outer ring having a plurality of cam
surfaces formed on an inner peripheral surface thereof, an inner member
mounted in said outer ring, a plurality of rollers mounted between said
respective cam surfaces and said inner member, and springs for urging said
rollers in a direction to provide engagement between said outer ring and
said inner member, said springs having a predetermined spring force which
is sufficient to maintain said rollers in engagement between said cam
surfaces and said inner member when a turning torque for turning said
inner member in a direction to urge said rollers out of said engagement is
applied to said inner member until the applied torque reaches a
predetermined value;
a cage mounted in said outer ring and formed with a plurality of pocket to
receive said rollers;
said cage providing spring guide surfaces for guiding a radial inner side
of said springs;
said outer ring having spring guide surfaces for guiding a radial outer
side of said springs and spring supporting surfaces for supporting ends of
said springs opposite to the ends of said springs near said rollers; and
said springs being supported in position by said spring supporting surfaces
of said outer member.
Description
The present invention relates to a torque limiter for selectively
transmitting torque and cutting off torque transmission, and more
particularly a torque limiter which can be used as a mechanism for
preventing sheets of paper from being fed with one sheet overlapping
another, provided in a paper feed roller unit or as a tension brake in a
mechanism for feeding a tape, ribbon or sheet.
Among the prior art torque limiters, a powder torque limiter and a spring
clutch type torque limiter are well-known. While the former has a high
performance, it is structurally complicated and thus costly. Also, it is
difficult to handle because it is integral with a shaft. The latter has a
problem that its on-off torque tends to fluctuate and its service life is
short.
In order to solve the problems with such prior art torque limiters, the
present inventors proposed in the Japanese Utility Model Application
63-55348 an improved torque limiter which utilizes the basic structure of
a one-way clutch and which can be manufactured at low cost.
As shown in FIG. 7, torque limiter of Japanese Utility Model Application
63-55348 comprises an outer ring 2 formed on its inner peripheral surface
with a plurality of clutch cam surfaces 1, a cage 3 of synthetic resin
mounted in the outer ring 2, rollers 4 held in spaces defined by the cage
3 and the cam surfaces 1, and S-shaped springs 6 fitted in recesses 7
formed in the cage 3 to bias the respective rollers 4 in such a direction
as to cause them to bite into between the clutch cam surfaces 1 and a
shaft 5 extending through the cage 3. The clutch cam surfaces 1, on which
the biasing force of the springs 6 and the roller 4 act, have such a wedge
angle that an on-off torque is produced as the shaft 5 rotates.
One problem in supporting the S-shaped springs 6 by the cage 3 made of
synthetic resin is that if the biasing force of the springs 6 is large, it
can deform the cage 3, thus causing the on-off torque to fluctuate.
It is an object of the present invention to provide a torque limiter which
obviates the abovesaid shortcomings, in which the distance between the
respective rollers and the spring supporting surfaces is kept unchanged,
and which is capable of preventing the fluctuation of on-off torque.
In accordance with the present invention, there is provided a torque
limiter comprising an outer ring formed on the inner peripheral surface
thereof with a plurality of clutch cam surfaces and spring supporting
surfaces, an inner member mounted in the outer ring, a plurality of
rollers mounted between the respective clutch cam surfaces and the inner
member, and springs supported on the spring supporting surfaces to bias
the rollers in such a direction as to bite into between the clutch cam
surfaces and the inner member.
The rollers are mounted between the clutch cam surfaces on the outer ring
and the outer peripheral surface of the inner member. The springs for
biasing the rollers in such a direction as to bite into between the clutch
cam surfaces and the inner member are supported on the supporting surfaces
formed on the inner peripheral surface of the outer ring. This makes it
possible to keep constant the distance between the respective rollers and
the spring supporting surfaces and to prevent the fluctuation of
deflection of the springs and thus the fluctuation of on-off torque.
By the provision of the inner ring as an inner member, different on-off
torque values can be attained with a smaller number of parts by combining
springs with rollers and inner rings of different sizes.
Other features and objects of the present invention will become apparent
from the following description taken with reference to the accompanying
drawings, in which:
FIG. 1 is a vertical sectional front view of the torque limiter embodying
the present invention;
FIG. 2 is a vertical sectional side view of the same;
FIG. 3 is an exploded perspective view of a portion of the same;
FIG. 4 is a view showing how the value of the required on-off torque is
set;
FIG. 5 is a vertical sectional side view showing the structure for
preventing the pin coupling the inner ring and the shaft together from
coming out;
FIG. 6 is an exploded perspective view of the same; and
FIG. 7 is a vertical sectional front view of a torque limiter according to
Japanese U. M. Application 63-55348.
Now referring to the drawings, the torque limiter according to the present
invention has basically the same construction as a one-way clutch. It
comprises an outer ring 11 formed on its inner peripheral surface with a
plurality of clutch cam surfaces 12, a cage 13 mounted in the outer ring
11 and formed with a plurality of pockets 16, an inner ring 14 mounted in
the cage 13, a plurality of rollers 15 disposed between the clutch cam
surfaces 12 on the outer ring 11 and the outer peripheral surface of the
inner ring and received in the respective pockets 16 formed in the cage
13, and springs 17 supported on supporting surfaces 18 formed on the inner
peripheral surface of the outer ring 11 to bias the rollers 15 in such a
direction as to bite into between the clutch cam surfaces 12 and the inner
ring 14.
The outer ring 11 has one end thereof closed by a lid 19 fitted on the
outer periphery of the inner ring 14. An outer member 20 made of synthetic
resin is put on the outer ring 11 to cover the outer peripheral surface
and the other end thereof as well as the outer periphery of the lid 19.
The inner ring 14 is coupled by a pin 22 to a shaft 21 extending
therethrough so as to turn with the shaft.
In the embodiment shown, the inner member comprises the shaft 21 and the
inner ring 14 mounted thereon. But the inner ring 14 may be omitted while
leaving only the shaft 21 to set the rollers 15 or the like between the
outer ring 11 and the shaft 21.
If the shaft 21 rotates in the direction of arrow A in FIG. 1, its rotation
is transmitted to the outer ring 11 through the rollers 15. If the shaft
21 rotates in the reverse direction, that is, the direction of arrow B,
its rotation will not be transmitted to the outer ring 11; in other words,
it will idle. Thus the torque limiter has the function of a one-way
clutch.
By adjusting the wedge angle of the clutch cam surfaces 12 and the biasing
force of the springs 17, the on-off torque with respect to the rotation of
the shaft 21 in the direction of arrow B, i.e. the torque at which the
shaft 21 begins to idle, can be set. Thus the torque limiter according to
the present invention can be used as a one-way torque limiter having means
for preventing backspin.
The metallic outer ring 11 is formed on its inner peripheral surface with
recessed portions 23 for receiving the springs 17 so as to be integral
with the clutch cam surfaces 12. Their respective end walls serve as the
supporting surfaces 18 for supporting the springs 17. With this
arrangement, the distance between the respective rollers 15 and the
supporting surfaces for the springs 17 can be held constant. This will in
turn serve to keep constant the biasing force of the springs 17 and thus
to prevent the fluctuation of the on-off torque.
By the provision of the inner ring 14 in the outer ring 11, the lid 19 and
the outer member 20 can be mounted thereon as shown in FIG. 2, to form a
torque limiter of a sealed type. This makes it possible to prevent the
leakage of grease and the admission of dust and thus to stabilize the
on-off torque for a prolonged period of time.
In order to minimize the fluctuation of on-off torque, it is important that
the surface of the member in contact with the rollers 15 have a required
roughness. By the provision of the inner ring 14, the surface roughness of
the outer peripheral surface of the inner ring can be controlled.
As shown in FIG. 2, the inner ring 14 and the shaft 21 are coupled together
so as not to be rotatable relative to each other by engaging a pin 22
extending diametrically through the shaft 21 in cutouts 31 formed in the
inner ring 14 at one end thereof at diametrically opposite positions.
In the example shown in FIGS. 5 and 6, a ring 32 is fitted on the outer
periphery of the inner ring 14 at the end thereof to prevent the pin 22
from coming out.
This ring 32 is made of synthetic resin and is press-fitted on the inner
ring 14 or bonded thereto to prevent the pin 22 from coming out.
The value of the on-off torque is determined by the biasing force of the
springs 17, the diameter of the rollers 15 and the outer diameter of the
inner ring 14 if the dimensions of the outer ring 11 are unchanged. The
on-off torque values required by users differ from one user to another. If
the parts are designed for every required on-off torque, a large number of
parts will have to be stocked.
In contrast, by preparing several kinds of springs 17 having different
biasing forces as well as rollers 15 and inner rings 14 having slightly
different dimensions from one another, various on-off torque values can be
attained with a smaller number of parts. The provision of the inner ring
14 serves to expand the range of attainable torque values and makes
possible more delicate torque control.
FIG. 4 shows by way of example how to set torque. The solid line illustrate
an inner ring 14 having an outer diameter D. The springs 17 used are ones
which give an on-off torque of 300 gf.cm if their height is H.
In order to meet the request for an on-off torque of 280 gf.cm, it is
necessary only to reduce their biasing force.
For this purpose, the inner ring 14 has to be replaced with one having such
an outer diameter D1 that the height of the springs will be H1.
Instead of changing the outer diameter of the inner ring 14 as shown in
FIG. 4, the adjustment of torque may be made by changing the diameter of
the rollers 15.
Even if it turns out in the final checkup that the torque value is off
specification, it can be corrected so as to be within specification by
replacing the inner ring with another one having a different outer
diameter.
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